Plumbum

Description

Plumbum

Plumbum Pharm. Lond. Lead: a pale, livid, soft, very flexible metal: above eleven times specifically heavier than water; fusible in a small heat, somewhat less than that in which expressed oils begin to boil. Continued in fusion it contracts a various-coloured pellicle on the surface, and if kept stirring, so as that fresh surfaces may be exposed to the air, it changes by degrees into a powdery dusky-coloured calx: this powder, calcined for some time in a stronger fire, in such a manner that the flame may reverberate all over it, becomes first yellow, and afterwards of a deep red colour †: all these calces, if the fire be hastily raised to a consider-able degree, melt into the appearance of oil, and on cooling form a soft flaky pulverable substanee called litharge ‡, of a pale yellowish or reddish colour, according as the lead has been less or more calcined: if the calces be urged with a pretty strong fire, they run into a yellowish glass, which, while in fusion, powerfully dissolves most kinds of earthy bodies, and corrodes the common crucibles till it has satu-rated itself with their earth.

The ores of lead, in colour commonly re-sembling lead itself, and of a cubical or paral-lelopipedal structure, are plentiful in England and other parts of the world. The metal, extracted from the ore by fusion, contains frequently a portion of silver, and sometimes of gold: on keeping the compound melted in a due degree of heat, the lead calcines and turns to litharge, which is raked or blown off till the noble metals remain pure; all the other common metallic bodies being scorified and carried off by the lead. From the works, wherein silver is thus extracted from lead in the large way, the shops are supplied with litharge; which, when pale coloured, is called litharge of silver; when high coloured, litharge of gold, The latter is to be preferred, not as containing any of the metal by whose name it is distinguished, but as being more thoroughly calcined than the pale sort: the pale may be freed from the uncalcined lead it holds, by melting it; the uncalcined part falling to the bottom during the fusion.

The nitrous acid, diluted with about an equal quantity of water, dissolves lead pretty readily into a gold-coloured liquor: by the vitriolic and marine acids it is very difficultly acted on; and when previously dissolved in the nitrous, it is by either of these precipitated. Vegetable acids, digested on lead in substance, dissolve it exceeding sparingly: by certain managements they may be made to act more vigorously, and to satiate themselves with the metal.

† Minium Ph. Lond.

‡ Lithargyrus Ph. Lond. & Ed.

Thin plates of lead, suspended over vinegar in a proper vessel, and set to digest in a gentle heat, as that of horfe-dung, that the acid vapour may rife and circulate round the plates, are found, in about twenty days, covered with a white powdery or flaky matter: this being scraped off, and the process repeated, the whole of the metal is thus corroded by degrees into ceruffe or white lead. This commodity, the preparation of which makes a considerable trade, is frequently adulterated with a mixture of whiting: the entire flaky masses, called flake lead, should be chosen, as not being liable to abuse. The adulteration may be discovered by means of vinegar, which will effervesce with and dissolve the whiting or calcareous earth: the liquor being then poured off clear, or filtered, the addition of a little spirit of salt will precipitate such part of the lead as the vinegar may have taken up; after which the calcareous earth will manifest itself on adding a little vitriolic acid.

The calces of lead are much easier of solu-tion in vegetable acids than lead in its metallic form. On digesting four ounces of litharge about three days in a sand heat with a pint of strong vinegar, and now and then making the vessel; the liquor, filtered, is found to have received a strong impregnation from the litharge, and to have dissolved about one tenth of it, whereas, of the same quantity of lead in sub-stance, scarcely one hundredth part would be dissolved. Lead even in its vitreous state, or in the glazing of the common earthen-ware vessels, is considerably acted on by vegetable acids; which, by being boiled in those vessels receive from them the peculiar taste, and pernicious qualities of saturnine solutions. - Lead may be discovered in acid liquors by a reddish, brown, or blackish colour being produced in them on adding a few drops of a solution of orpiment or common sulphur made in lime-water, and by the colour not being destroyed on the super-addition of a little spirit of salt (a): other metals, dissolved in vegetable acids, produce, as well as lead, a dark colour with the sulphu-reous solutions, but spirit of salt redissolves them, and totally discharges the colour.

Ceruffa Ph. Lond. & Ed.

Actetum li-thargyrites.

Of all the saturnine calces, the cerusse, on account of the corrosion it has previously undergone from the steam of vinegar, is the most easily dissoluble in fresh vinegar, and hence is made choice of where a saturated solution is required. The solution made in vinegar, in-fpiffated to the consistence of honey and set in the cold, shoots by proper management into crystals, called, from their taste, sugar of lead. All the solutions, and soluble preparations of this metal, have a remarkably sweet taste, mixed with a considerable austerity.

Lead in its metallic form, or when calcined by fire, does not appear to have any medicinal operation: dissolved or rendered soluble by acids, it is one of the most powerful styp-tics, but at the same time, for internal uses, one of the most: dangerous. A few grains of the sugar have been ventured on for checking obstinate hemorrhagies and other profuse evacuations: a tincture drawn with rectified spirit, by maceration without heat, from sugar of lead and green vitriol, in the proportion of three ounces of the sugar and two of the vitriol, to a quart of spirit, has been given from fifteen to thirty drops, for restraining the colliquative sweats attending phthises and hectic fevers. This practice has in some instances been successful, but the hazard is very great: all the saturnine preparations that have any activity are in a peculiar manner injurious to the nervous system, and ought never to be ventured on but in des-perate cases as a last resource. Obstinate con-stipations, violent colics, pains and contractions of the limbs, tremors and resolutions of the nerves, and slow wasting fevers, are the general consequences of saturnines taken in any consi-derable quantities internally, and of the fumes to which the workmen are exposed in the fusion of the metal in the way of business(a).